openldap/doc/guide/admin/maintenance.sdf

# $OpenLDAP$
# Copyright 2007-2011 The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.

H1: Maintenance

System Administration is all about maintenance, so it is only fair that we 
discuss how to correctly maintain an OpenLDAP deployment.


H2: Directory Backups

Backup strategies largely depend on the amount of change in the database
and how much of that change an administrator might be willing to lose in a 
catastrophic failure. There are two basic methods that can be used:

1. Backup the Berkeley database itself and periodically back up the transaction 
log files:

Berkeley DB produces transaction logs that can be used to reconstruct
changes from a given point in time. For example, if an administrator were willing to only
lose one hour's worth of changes, they could take down the server in
the middle of the night, copy the Berkeley database files offsite, and bring
the server back online. Then, on an hourly basis, they could force a
database checkpoint, capture the log files that have been generated in the
past hour, and copy them offsite. The accumulated log files, in combination
with the previous database backup, could be used with db_recover to
reconstruct the database up to the time the last collection of log files was
copied offsite. This method affords good protection, with minimal space
overhead.


2. Periodically run slapcat and back up the LDIF file:

Slapcat can be run while slapd is active. However, one runs the risk of an
inconsistent database- not from the point of slapd, but from the point of
the applications using LDAP. For example, if a provisioning application
performed tasks that consisted of several LDAP operations, and the slapcat
took place concurrently with those operations, then there might be
inconsistencies in the LDAP database from the point of view of that
provisioning application and applications that depended on it. One must,
therefore, be convinced something like that won't happen. One way to do that
would be to put the database in read-only mode while performing the
slapcat. The other disadvantage of this approach is that the generated LDIF
files can be rather large and the accumulation of the day's backups could
add up to a substantial amount of space.

You can use {{slapcat}}(8) to generate an LDIF file for each of your {{slapd}}(8) 
back-bdb or back-hdb databases.

>    slapcat -f slapd.conf -b "dc=example,dc=com"

For back-bdb and back-hdb, this command may be ran while slapd(8) is running.

MORE on actual Berkeley DB backups later covering db_recover etc.

H2: Berkeley DB Logs

Berkeley DB log files grow, and the administrator has to deal with it. The 
procedure is known as log file archival or log file rotation. 

Note: The actual log file rotation is handled by the Berkeley DB engine.

Logs of current transactions need to be stored into files so that the database 
can be recovered in the event of an application crash. Administrators can change 
the size limit of a single log file (by default 10MB), and have old log files 
removed automatically, by setting up DB environment (see below). The reason 
Berkeley DB never deletes any log files by default is that the administrator 
may wish to backup the log files before removal to make database recovery 
possible even after a catastrophic failure, such as file system corruption.

Log file names are {{F:log.XXXXXXXXXX}} (X is a digit). By default the log files 
are located in the BDB backend directory. The {{F:db_archive}} tool knows what 
log files are used in current transactions, and what are not. Administrators can 
move unused log files to a backup media, and delete them. To have them removed 
automatically, place set_flags {{DB_LOG_AUTOREMOVE}} directive in {{F:DB_CONFIG}}. 

Note: If the log files are removed automatically, recovery after a catastrophic 
failure is likely to be impossible.

The files with names {{F:__db.001}}, {{F:__db.002}}, etc are just shared memory 
regions (or whatever). These ARE NOT 'logs', they must be left alone. Don't be 
afraid of them, they do not grow like logs do.

To understand the {{F:db_archive}} interface, the reader should refer to 
chapter 9 of the Berkeley DB guide. In particular, the following chapters are 
recommended:

* Database and log file archival - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/archival.html}}
* Log file removal - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/logfile.html}}
* Recovery procedures - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/recovery.html}}
* Hot failover - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/ref/transapp/hotfail.html}}
* Complete list of Berkeley DB flags - {{URL:http://www.oracle.com/technology/documentation/berkeley-db/db/api_c/env_set_flags.html}}

Advanced installations can use special environment settings to fine-tune some 
Berkeley DB options (change the log file limit, etc). This can be done by using 
the {{F:DB_CONFIG}} file. This magic file can be created in BDB backend directory 
set up by {{slapd.conf}}(5). More information on this file can be found in File 
naming chapter. Specific directives can be found in C Interface, look for 
{{DB_ENV->set_XXXX}} calls.

Note: options set in {{F:DB_CONFIG}} file override options set by OpenLDAP. 
Use them with extreme caution. Do not use them unless You know what You are doing.

The advantages of {{F:DB_CONFIG}} usage can be the following:

* to keep data files and log files on different mediums (i.e. disks) to improve 
  performance and/or reliability;
* to fine-tune some specific options (such as shared memory region sizes);
* to set the log file limit (please read Log file limits before doing this).

To figure out the best-practice BDB backup scenario, the reader is highly 
recommended to read the whole Chapter 9: Berkeley DB Transactional Data Store Applications. 
This chapter is a set of small pages with examples in C language. Non-programming 
people can skip these examples without loss of knowledge.


H2: Checkpointing

MORE/TIDY

If you put "checkpoint 1024 5" in slapd.conf (to checkpoint after 1024kb or 5 minutes, 
for example), this does not checkpoint every 5 minutes as you may think. 
The explanation from Howard is:

'In OpenLDAP 2.1 and 2.2 the checkpoint directive acts as follows - *when there 
is a write operation*, and more than <check> minutes have occurred since the 
last checkpoint, perform the checkpoint. If more than <check> minutes pass after 
a write without any other write operations occurring, no checkpoint is performed, 
so it's possible to lose the last write that occurred.''

In other words, a write operation occurring less than "check" minutes after the 
last checkpoint will not be checkpointed until the next write occurs after "check" 
minutes have passed since the checkpoint.

This has been modified in 2.3 to indeed checkpoint every so often; in the meantime 
a workaround is to invoke "db_checkpoint" from a cron script every so often, say 5 minutes. 

H2: Migration

The simplest steps needed to migrate between versions or upgrade, depending on your deployment
type are:

.{{S: }}
^{{B: Stop the current server when convenient}}

.{{S: }}
+{{B: slapcat the current data out}}

.{{S: }}
+{{B: Clear out the current data directory (/usr/local/var/openldap-data/) leaving DB_CONFIG in place}}

.{{S: }}
+{{B: Perform the software upgrades}}

.{{S: }}
+{{B: slapadd the exported data back into the directory}}

.{{S: }}
+{{B: Start the server}}

Obviously this doesn't cater for any complicated deployments like {{SECT: MirrorMode}} or {{SECT: N-Way Multi-Master}}, 
but following the above sections and using either commercial support or community support should help. Also check the
{{SECT: Troubleshooting}} section.